After you get the end, the main menu allows you to replay any of the levels that you want but you're right that you would have to start from the beginning again to get the power-ups back. Thanks for the feedback though, we're glad you took the time to try out what we made.
I’d encourage you not to think of dying as a failure :) Just try to collect as many pixies as you can. If you get 20-30, you’ve done well. Collecting all 49 takes a lot of practice!